When the operators do not have enough information on the vessel's stability and freeboard, it is recommended that they keep the ballast tank empty in full load operating condition and do not exceed that load before consulting a design architect. The tugboat had been designed as a harbour vessel and her fresh water tank capacity was limited. To complement the on-board potable water capacity during long voyages, present and former crews had cement-washed the ballast tank and filled it with fresh water. Photographs taken shortly before the beginning of the vessel's last voyage show that the vessel met the single-compartment flooding criterion of current regulations. These regulations prescribe that no part of the main deck be submerged in the event of flooding of any single watertight compartment located aft of the engine-room and they call for the retention of positive buoyancy and transverse stability. It was believed that the piping of the overboard discharge of the bilge pump and fire pump was too small for the two pumps to be operated simultaneously. Critical time was lost when the bilge pump was stopped and valves were switched to pump the ballast tank. Evidence indicates that the storeroom flooded between 2200 and 2235, a time lapse of only half an hour. Since the storeroom contained approximately 27,776litres of water, the rate of flooding had to have been in excess of 54,552litres/hr. This rate of flooding was beyond the hydraulic capacity of the pumping system. A maximum head of water in excess of 2.13m was created in the storeroom when it flooded, and the main shaft gland at the bulkhead did not prevent the progressive flooding of the engine-room. On small vessels, there is a tendency to call each crew member individually when an emergency arises. The emergency message must be repeated and critical time is wasted. A proper signal on the ship's whistle simplifies the task of mustering all of the crew and provides to all crew members an equal amount of time to proceed to the life-saving appliances. The ClassI EPIRB had been properly armed and proved operational when it floated to the surface, but the ClassII EPIRBs were not brought aboard the liferaft, although they should have been as a precautionary measure. Two of the immersion suits from one of the manufacturers were especially appreciated because the boots were a tight fit and the mittens were separated from the sleeves. The life-saving appliances could therefore be handled with bare hands, thus facilitating the task of launching the lifeboat.Analysis When the operators do not have enough information on the vessel's stability and freeboard, it is recommended that they keep the ballast tank empty in full load operating condition and do not exceed that load before consulting a design architect. The tugboat had been designed as a harbour vessel and her fresh water tank capacity was limited. To complement the on-board potable water capacity during long voyages, present and former crews had cement-washed the ballast tank and filled it with fresh water. Photographs taken shortly before the beginning of the vessel's last voyage show that the vessel met the single-compartment flooding criterion of current regulations. These regulations prescribe that no part of the main deck be submerged in the event of flooding of any single watertight compartment located aft of the engine-room and they call for the retention of positive buoyancy and transverse stability. It was believed that the piping of the overboard discharge of the bilge pump and fire pump was too small for the two pumps to be operated simultaneously. Critical time was lost when the bilge pump was stopped and valves were switched to pump the ballast tank. Evidence indicates that the storeroom flooded between 2200 and 2235, a time lapse of only half an hour. Since the storeroom contained approximately 27,776litres of water, the rate of flooding had to have been in excess of 54,552litres/hr. This rate of flooding was beyond the hydraulic capacity of the pumping system. A maximum head of water in excess of 2.13m was created in the storeroom when it flooded, and the main shaft gland at the bulkhead did not prevent the progressive flooding of the engine-room. On small vessels, there is a tendency to call each crew member individually when an emergency arises. The emergency message must be repeated and critical time is wasted. A proper signal on the ship's whistle simplifies the task of mustering all of the crew and provides to all crew members an equal amount of time to proceed to the life-saving appliances. The ClassI EPIRB had been properly armed and proved operational when it floated to the surface, but the ClassII EPIRBs were not brought aboard the liferaft, although they should have been as a precautionary measure. Two of the immersion suits from one of the manufacturers were especially appreciated because the boots were a tight fit and the mittens were separated from the sleeves. The life-saving appliances could therefore be handled with bare hands, thus facilitating the task of launching the lifeboat. The ballast tank was supposed to be kept empty under full load operating condition, but it was filled with potable water. Transport Canada had conducted an intermediate inspection of the tugboat at the beginning of the navigation season. On departure, the total deadweight and mean draught were greater than those indicated under the fully loaded condition shown in the vessel's stability data. The storeroom was the first compartment to flood. The source of the ingress of water and the cause of the flooding of the storeroom remain unknown. The vessel's pumping system was not used to maximum capacity. The rate of flooding was greater than the vessel's maximum pumping capacity. The ClassII EPIRBs were not used.Findings The ballast tank was supposed to be kept empty under full load operating condition, but it was filled with potable water. Transport Canada had conducted an intermediate inspection of the tugboat at the beginning of the navigation season. On departure, the total deadweight and mean draught were greater than those indicated under the fully loaded condition shown in the vessel's stability data. The storeroom was the first compartment to flood. The source of the ingress of water and the cause of the flooding of the storeroom remain unknown. The vessel's pumping system was not used to maximum capacity. The rate of flooding was greater than the vessel's maximum pumping capacity. The ClassII EPIRBs were not used. The JMANIC sank because an ingress of water gradually reduced the vessel's longitudinal stability and reserve buoyancy. The vessel's freeboard and reserve buoyancy were reduced when the ballast tank was filled with fresh water. The source of the ingress of water and the cause of the flooding remain unknown.Causes and Contributing Factors The JMANIC sank because an ingress of water gradually reduced the vessel's longitudinal stability and reserve buoyancy. The vessel's freeboard and reserve buoyancy were reduced when the ballast tank was filled with fresh water. The source of the ingress of water and the cause of the flooding remain unknown.